A partner of my company (not sure whether i can tell their name here - i´ll use example.com instead) asked me yesterday, why there is such a big difference when they enter the site command at google at first with "www" and then without "www", to check the number of indexed pages.

First of all, the Google Webmaster Tools show about 9.000.000 indexed pages.

"site:example.com" provides me about 10.000.000 hits.
"site:www.example.com" are only about 4.000.000 hits.

I first thought that they have some subdomains registered, such as "blog.example.com", or "test.example.com" ...
But entering "site:example.com -site:www.example.com" to detect pages from subdomains other than www, brings up exactly 2 hits.
Where are the other 6.000.000 ?

The next thing is, providing google a little bit more in the query such as "site:www.example.com in" (or other linking words) brings me more hits than the blank site command with www ("site:www.example.com"). Sometimes about 2.000.000 more than the blank www query...

site: queries attempt to estimate how many pages are in our index, but we would never claim that it is an exact amount that is completely accurate. ...Once you get past a few thousand pages, that is not all that useful as a metric.

We try to be very clear that our results estimates are just that--estimates. In theory we could spend cycles on that aspect of our system, but in practice we have a lot of other things to work on, and more accurate results estimates is lower on the list than lots of other things.

+1 The results of site: are explicitly not promised to be complete. (Read: It's not really a matter of "reliability" so much as that your expectations are wrong.) If you want to know how many pages are indexed for your site, that's what Webmaster Tools is for.
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Su'Apr 11 '13 at 9:44

Thanks. I also believe that our best choice is believing the numbers from the webmaster tools. With the above information given, i think i understand a little bit more about these circumstances
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limepixApr 12 '13 at 7:17